For environmental protection and personnel safety, spray booths are normally used in commercial paint spraying operations to collect paint overspray and evaporated paint solvents. In one type of spray booth, the paint overspray and air circulated through the booth is contacted with water. The air is scrubbed with the water to decrease stack emissions. The water and entrained paint and solvent circulated through the booth flow to a tank and hence are recirculated through the booth. The paint tends to float on the water and forms a sticky mass which tends to coat the walls of the spray booth and pumps, headers, nozzles and venturis. Frequent maintenance is required to clean the spray booth to keep it operating efficiently. As paint deposits decrease the operational efficiency of a booth, stack emissions increase. Spray booth maintenance can be reduced by adding chemicals to the water to cause the paint to coagulate into non-tacky solid particles which can sink in the tank and accumulate at the bottom of the tank as a sludge. In some spray booths, liquid in the tank is highly agitated to maintain the sludge in suspension during operation. Unless removed by other means, the spray booth must be shut down periodically, drained and the sludge is manually removed from the tank. The liquid removed from the spray booth tank is considered hazardous waste because of the paint, paint solvent and chemicals in the liquid. Disposal of this waste is quite expensive since it contains large amounts of water. For high production systems, frequent maintenance is required.
An improved water wash spray booth system is shown in U.S. Pat. No. 4,696,254. In this system, liquid including water, chemical additives and paint sludge flows from a number of spray booths to a sludge pit. In the pit, the liquid is continuously recirculated and agitated by a first pump to maintain the sludge in suspension. A second pump circulates liquid from the sludge pit through a hydrocyclone separator to separate the solids from the liquid and the clarified liquid from the separator is returned to the sludge pit. The solids are collected in a barrel along with a small quantity of liquid. A portion of the pit liquid from the second pump outlet also is circulated through an aspirator or siphon pump and back to the pit. The aspirator pump removes excess liquid from the sludge collection barrel. Since liquid containing paint sludge is circulated through the aspirator pump, the pump will require periodic maintenance. The expense of disposing of the hazardous waste from the spray booth may be significantly reduced by this system since most of the water has been removed from the waste sludge in the barrel.